bash: add element before each element of an array

Question

I have an array of strings, like:

ARR=(aa bb "cc dd")

I want to call an executable with parameter like:

my_executable -f aa -f bb -f "cc dd"

So I need to add a prefix -f to each element of ARR. I did a search and find:

${ARR[@]/#/-f }

However, this will generate something like:

-f aa -f bb -f cc dd

And if I use my_executable ${ARR[@]/#/-f }, it will pass 7 instead of 6 arguments to my_executable. If I double quote the string substitution part, it will generate 3 arguments, i.e. "-f aa" "-f bb" "-f cc dd", which is not what I want either.

How can I do to make it work? Thank you!

devnull · Accepted Answer · 2014-03-16 19:55:12Z

5

You could create a new array with the elements inserted. Pass the arguments to the program by saying:

"${NEWARR[@]}"

Given your example:

ARR=(aa bb "cc dd")
NEWARR=()
for i in "${ARR[@]}"; do
  NEWARR+=(-f)
  NEWARR+=("$i")
done
for i in "${NEWARR[@]}"; do
  echo "$i";
done

this would produce:

-f
aa
-f
bb
-f
cc dd

_{Make sure that you quote your variables.}

edited Mar 16, 2014 at 19:55

answered Mar 16, 2014 at 19:38

devnull

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5 Comments

james Over a year ago

Thank you for your answer. It seems that NEWARR now has 3 elements, "-f aa" "-f bb" "-f cc dd". But I want it to have 6 elements, -f aa -f bb -f "cc dd". I'm sorry, the title was misleading. I have changed the title.

jaypal singh Over a year ago

@devnull Now thats slick!

devnull Over a year ago

@jaypal Stupid things happen!

Adrian Frühwirth Over a year ago

+1, I'd save a line by adding both elements at once doing NEWARR+=('-f' "${i}"), though.

devnull Over a year ago

@AdrianFrühwirth That's a good option. However, an extra line wouldn't hurt for the sake of clarity.

Xen2050 · Accepted Answer · 2014-03-17 00:40:44Z

0

How about building the argument list as a string that you use to run my_executable?

for i in "${ARR[@]}"do
  arglist+="-f \"$i\" "
done

This will quote all the elements in your array ARR, without quoting the -f (if that matters).

echo $arglist -f "aa" -f "bb" -f "cc dd"

Then you can use

my_executable $arglist

answered Mar 17, 2014 at 0:40

Xen2050

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